Energy-efficiency and maintenance are fundamental design criteria for the development of wireless standards for the future Internet of Things. This is typically achieved by designing asymmetric communication links. Battery-powered devices with low complexity, low cost, and low computational capabilities are wirelessly connected to powerful devices with high complexity, cost, and computational capabilities. Examples of short range technologies based on this paradigm are Bluetooth Low Energy (BLE), WiFi, and ZigBee.
BLE is a wireless personal area network technology based on single-hop client/server type of connections. Compared to Classic Bluetooth, BLE is intended to provide considerably reduced power consumption and cost. The Bluetooth SIG identifies a number of markets for BLE technology, particularly in the smart home, health and fitness sectors, with a great potential as an enabling technology for the Internet of Things.
A low power network is composed of a number of powerful routers and battery-powered end-devices. For applications such as smart home and fitness, low latency is not a stringent requirement. Sensed information or actuation commands require time constraints in the order of hundreds of milliseconds, which is of orders of magnitude larger than the typical time on the air for the corresponding generated packets.
In order to save energy and avoid costly centralized management, devices use asynchronous communication and contention-based channel access. As an example, BLE allows devices to communicate information through advertisement messages sent in the air, without establishing a data connection. An end device is usually powered with a low capacity battery with reduced computation power. Routers by contrast are usually mains powered and provide message forwarding, rerouting and self-healing functionalities for the established network. In order to discover routers in the neighborhood, or update information to the current router in the neighborhood, end-devices need to exchange signaling messages with such routers. When advertisement messages are used for such signaling messages, there are standard rules to comply with.
For BLE, the specifications set a minimum interval between consecutive advertising events, and this interval varies depending on the type of advertisement from few to hundreds of milliseconds. According to the current BLE specification, if an end-device sends a request message to a router that is engaging communications through advertisements, the end-device needs to wait before getting a response for a time that depends on the minimum interval between consecutive advertising events in the router side. In the worst case, if the router has just sent an advertisement right before receiving the request message, it needs to wait a time equal to the interval between consecutive advertising events before sending the response.